1. Field of the Invention
The present invention relates to a device for preventing dew condensation in a container, and more particularly, to a device for preventing dew condensation in a space inside a container used for transporting goods by, e.g., truck or ship.
2. Description of the Related Art
In general, a container is used for transporting a large amount of goods, and according to international regulations, such a container has a long side length of 6 meters or 12 meters, and a short side length of about 2.5 meters. The container has a predetermined inner volume, and has an outer wall made of a metal material. Due to the construction of the container, however, dew condensation is easily generated therein.
To prevent the forming of dew condensation in the container, the following techniques have been proposed.
(1) A container is constructed so that the temperature or humidity therein can be controlled. PA1 (2) Ventilation holes are provided in the side walls of the container, to provide an internal ventilation thereof. PA1 (3) A disposable anti-wetting sheet or desiccant is provided in the container, for eliminating moisture inside the container. PA1 a container body having a generally rectangular parallelepiped shape with outer walls defining a space therebetween for storing goods; PA1 said outer walls also defining an intake opening for an introduction of an atmospheric air into the space of the container, and an exhaust opening for a removal of the air from the inside space of the container to the atmosphere; PA1 the intake and the outlet openings being provided at different locations inside the container; PA1 a fan for generating a forced flow of air from the intake opening to the exhaust opening, via the inside space of the container; PA1 a sensor for detecting a temperature inside the container and issuing electric signals indicating the detected temperature; PA1 means for determining if a change in the detected temperature over a unit of a time is larger than a predetermined value, and; PA1 control means for operating the fan when said determination is positive. PA1 a container body having a generally rectangular parallelepiped shape with outer walls defining a space therebetween for storing goods; PA1 said outer walls also defining an intake opening for an introduction of an atmospheric air into the space of the container, and an exhaust opening for a removal of the air from the inside space of the container to the atmosphere; PA1 the intake and the outlet openings being provided at different locations on the walls of the container; PA1 a fan for generating a forced flow of an air from the intake opening to the exhaust opening, via the inside space of the container; PA1 a first temperature sensor for detecting a temperature at the walls of the container; PA1 a second temperature sensor for detecting a temperature of the air inside the container; PA1 a first determining means for determining if the wall temperature detected by the first sensor is lower by a predetermined value than the air temperature detected by the second sensor; PA1 second determining means for determining if a change in the wall temperature detected by the first sensor means over a unit of a time is larger than a predetermined value, and; PA1 control means for operating the fan when one of said determinations is positive.
The prior art techniques listed above for eliminating moisture in the container have several drawbacks. Namely, solution (1) requires a special control device for realizing a suitably designed refrigerating cycle for the space inside the container, and thus the container must have a special and expensive construction. Furthermore, the control device for realizing a refrigeration cycle mounted in the container requires a power to be supplied from a suitable outside appliance, which is not always available in a given situation.
The solution (2) obtains a ventilation effect by using a temperature difference between the inside and outside of the container, and thus ventilation holes having a small opening do not provide a desired ventilation. If the ventilation holes have a large opening, outside water, such as rain water, can enter the space inside the container via the holes, and therefore, a specially designed device must be fitted to prevent this introduction of the outside water, which makes the system expensive.
The solution (3) is disadvantageous in that a large amount of desiccant is required since the space inside the container is under a condition such that dew condensation is very easily generated, resulting an increase in the cost due to the desiccant. Furthermore, the use of the desiccant alone does not fully prevent dew condensation over the entire region of the large space inside the container.
Another prior art, Japanese Unexamined Patent Publication No. 1-26044, discloses a device for preventing dew condensation in the home. This device is provided with a humidity sensor arranged in a room and issuing an electric signal indicating a degree of humidity therein, for operating a ventilation apparatus. Further, Japanese Unexamined Patent Publication 2-178546 discloses a device provided with a temperature sensor arranged in a room and issuing a signal indicating a need for operating a ventilation apparatus. These prior art types of ventilation apparatus for a house are sufficient to prevent dew condensation therein, since the walls and ceilings of a house are usually made of a heat insulating material, which can prevent a quick change of the temperature therein irrespective of a change in the atmospheric temperature, and thus a relatively long time must lapse before dew condensation is formed. Therefore, a mere detection of the humidity or the temperature is sufficient to prevent the occurrence of dew condensation.
Unlike a house, however, a container to which the present invention is related is used under very severe conditions from the view point of temperature, and the inventor found that a control of the ventilation apparatus by a detection of the temperature only will not prevent a forming of dew condensation in the container, because the temperature inside the container changes very rapidly.